Control system



Oct. 9, 1934. D. c. PRINCE CONTROL SYSTEM Filed Nov. 30. 1931 Figl.

l lmrm nnrm Patented Oct. 9, 1934 PATENT OFFICE CONTROL SYSTEM David 0.Prince, Swarthmore, Pa., assignor to General Electric Company, acorporation of New York Application November 30, 1931, Serial No.577,885

9 Claims.

My invention relates to control systems wherein a variable sourceoflight is utilized and more particularly to means for controlling thetemperature of electric furnaces and the like, and has I for its objectthe provision of a simple and reliable means for varying the inputenergy to an electric furnace to maintain the temperature of the furnaceat a predetermined value.

More particularly my invention relates to temlo perature control systemsemploying radiant energy from the furnace or other heated device toactivate alight sensitive control device, although it obviously hasgeneral application in control systems where a variable source of lightis utilized. ll It is an object of my invention to provide a controlsystem of this type giving uniform and accurate response independentlyof variations in the operating characteristics of the light sensitivedevice. so In accordance with my invention in one form thereof, Iprovide means for controlling the temperature of an electric furnace inresponse to the relative intensity of the light radiated from thefurnace and from a standard source of light. My invention alsocomprehends a control system for an electric valve wherein the electricvalve is controlled in response to the relative intensities of aplurality of light sources, one of which is variable.

For a more complete understanding of my invention, reference should behad to the accompanying drawing, Fig. 1 of which is a diagrammaticrepresentation of a temperature control system for a furnace embodyingmy invention, while Figs. 2-5, inclusive, illustrate curves explanatoryof the operation of my invention.

Referring to the drawing, I have shown my invention in one form asapplied to the control of an electric furnace provided with a heatingresistor 11 which is connected through the coils l2 and 13 of asaturable core reactor 14 to a suitable source of alternating currentsupply as is indicated by the supply lines 15 and 16. The reactor 14 isalso provided with a coil 17 connected in the output circuit of anelectric valve 18, preferably of the type having an inert gas, such asmercury vapor within its envelope and sometimes termed a grid controlledarc rectifier. It will be understood that when the grid 19 is madesumciently positive when its anode 20 is positive the valve or rectifier18 becomes conductive. As shown a battery 21 is connected in the gridcircuitso as to maintain the grid 19 sumciently negative normally toprevent the passage of current through the valves. In order to renderthe valve 18 conductive under certain conditions of operation, alightsensitive device 22 is connected through a battery 23 to the primarywinding 24 of a transformer 25, the secondary 26 of which is connectedin the grid circuit of the rectifier.

The temperature of the furnace is controlled by comparing the amount ofintensity of light from the furnace with the amount of intensity of thelight of a standard source of radiation 27. As shown, the comparison ismade by means of a 55 rotatably mounted mirror 29 provided with fourreflecting surfaces arranged at right angles with each other to form acube.

With the mirror29 occupying the full line position one of its reflectingsurfaces serves to di- 7 rect light from a tube 31 extending within thefurnace 10 to the light sensitive device 22. This tube 31 may bedirected to a point on the wall of the furnace and as will be understoodby those skilled in the art, the intensity of the light con- 7 ductedthrough the tube 31 to the mirror 29 will vary with the temperature ofthe furnace.

If the mirror occupies the position illustrated by the broken lines,light will be directed from the standard 27 to the light sensitivedevice 22. By rotating the mirror 29 at a speed such that the radiationfrom the standard 27 is thrown on the light sensitive device 22 whilethe anode voltage of the rectifier 18 is positive and the radiation fromthe standard 27 is directed to the device 22 while the anode isnegative, the valve or rectifier 19 may be controlled in a manner togovern the temperature of the furnace 10. A synchronous motor 33 istherefore employed to drive the mirror 29. The motor 33 is connected byconductors 34 and 35 across the anode supply lines 15 and 16.

The anode or plate 20 is connected by a conductor 36 to the secondary 37of a transformer 38, the primary 39 of which is connected to the supplylines 15 and 16.

With the above understanding of the elements and their organization withrespect to each other in the system, the operation of the system itselfand the manner in which the light sensitive device 22 accuratelycontrols the temperature of the furnace 10 due to the difierence in theintensity of the, light rays from the furnace with the light rays fromthe standard will be readily understood from the description whichfollows:

It. will be assumed that the supply lines 15 and 16 are suitablyenergized from an alternating current source of supply (not shown) andthat the standard light source 27 has been adjusted by means of thebattery 32 to produce radiant energy having an intensity the same as theradiant en- 1 ergy directed by the tube 31 on the light sensitive device22 when the temperature of the furnace has reached a predeterminedvalue. As I have stated, the motor 33 drives synchronously the mirror 29with respect to the anode voltage so that the light from the standard 27is directed to the light sensitive device 22 during one half of a cycleof anode voltage while light from the furnace 10 is directed to thedevice 22 during the other half cycle of anode voltage.

Referring now to Fig. 2, the anode voltage is represented by the curve40, while in Fig. 3 the condition is represented when the furnace iscold and consequently no light rays from the furnace are directed to thelight sensitive device 22 during the negative half cycle of anodevoltage. However, during the positive half of the cycle, the light raysfrom the standard are directed on the device 22 to cause a response fromthe photoelectric cell which, for the sake of clarity of description, isrepresented by the straight lines 41 and 42. The resulting voltage waveobtained at the terminals of the secondary winding 26 of the transformer25 may therefore be represented by drawing a sinusoidal like curve 43with the zero axis represented by the broken line 44 half way betweenthe line 41 and the line 45 representing the zero axis.

It will be observed that the positive half of the cycle occurs while theanode is positive. The transformer 25 is therefore connected so that thegrid 19 of the rectifier 18 is caused to be positive when the anode 20is positive. The rectifier 18 therefore becomes conductive andsaturating current flows through the coil 17 of the reactor 14.

Consequently the reactor permits current to flow through its coils 12and 13 to the heating resistance 11.

As soon as the temperature of the furnace 10 increases radiant energy isproduced which is directed on the device 22. This condition isrepresented in Fig. 4. During the negative half of the cycle of anodevoltage the light rays from the furnace are directed on the device 22 tocause the light sensitive device 22 to respond as indicated by the lines46 and 47. The response of the device 22 due to the radiation from thestandard 27 remains the same as before and is againrepresented by thelines 41 and 42.

The resulting wave form 48 of secondary voltage has the same phaserelation with respect to the anode voltage as before but its amplitudehas been decreased due to the response of the device 22 to theradiations from the furnace.

As soon as the temperature of the furnace increases so that itsradiation as directed on the light sensitive device 22 is greater thanthat of the standard 2'7, the phase of the grid voltage reverses andcontrol of the electric valve 18 is thereby obtained. This condition isrepresented in Fig. 5, the lines 41 and 42 again representing theresponse of the device 22 to the standard, while the lines 49 and 50represent the response from the furnace radiation. In this case it willbe observed that the peak of the voltage wave 51 of the secondaryvoltage occurs during the negative half cycle of anode voltage while inthe previous cases (Figs. 3 and 4) the peak occurred during the positivehalf cycle of anode voltage. The result is a reversal in the phase ofthe grid voltage with respect to its anode voltage, which reversalrenders the valve or rectifier 18 non-conductive. Consequently thesaturation of the reactor 14 disappears thereby substantially preventingcurrent flow through the heating resistance 11.

The control of the heating current or the rate of heat generationtherefore depends on the relative intensities of the light rays from thestandard 22 and the furnace 10. The effect of any variations in theresponse of the light sensitive device 22 as well as any variations ofvoltage of the battery 23 do not affect the temperature control of thefurnace because it is the relative light radiation that eil'ectuates thetemperature control of the furnace. In other words the response of thelight sensitive device to the two sources of light will vary by equalamounts and result in the same grid control voltage for a given relativeintensity of the two light sources, regardless of the sensitivity of thedevice 22.

It will be observed that the amount of light received by the device 22is not constant over a half cycle of anode voltage. In the positionsshown, the maximum amounts of light are directed to the light sensitivedevice 22. For instance, considering the full line position of themirror it will be seen that the intensity gradually decreases as themirror is rotated until no light from the furnace is directed to thedevice 22. In the same manner, the light directed by the mirror 29 fromthe standard 27 gradually increases to a maximum and then decreases tozero.

While I have described what I at present consider the preferredembodiment of my invention, it will be obvious to those skilled in theart that various changes and modifications may be made without departingfrom my invention and I, therefore, aim in the appended claims to coverall such changes and modifications as fall withk vided with input andoutput circuits, a source of alternating current supply for said outputcircuit, a standard source of light, a variable source of light, andmeans including a light sensitive member and a member for directinglight thereto alternately from said standard source and from saidvariable source for impressing an alternating voltage on the inputcircuit of said valve varying in phase relation with respect to thevoltage of said alternating current supply in accordance with therelative intensities of the light from said standard source an from saidvariable source. 2. In a control system, a grid controlled electricvalve provided with input and output circuits, a source of alternatingcurrent supply for said source of alternating current for successive- 1ydirecting light from said sources to said light sensitive device, andmeans responsive to said light sensitive device for impressing on saidinput circuit a voltage varying in phase relation with respect to thevoltage of said source of alternating current in accordance with therelative intensities of the light from said standard source and fromsaid variable source.

3. In combination, a furnace, a heating resistor therefor, a gridcontrolled electric valve the conductivity of which is arranged to becontrolled by variation of the phase relation between the grid and anodevoltages, means responsive to said valve for controlling theenergization of said resistor, a standard source of light rays, a lightsensitive device, means for alternately directing light rays from saidfurnace and from' said standard source to said light sensitive device,and means responsive to said light sensitive device for varying thephase relation between the grid-and anode voltage of said valve.

4. A temperature control system comprising a furnace, a heating resistortherefor, a reactor for controlling the heating current of saidresistor, a grid controlled rectifier for controllin the degree ofsaturation of said reactor, a source of alternating current for theanode of said rectifler, a standard source of light and means includinga light sensitive device responsive to radiations .from said furnace andfrom said standard for controlling the phase relation between said gridand anode voltages whereby the saturation of said reactor is controlledso as to maintain a substantially constant temperature within saidfurnace.

5. In combination, a furnace, a heating resistor therefor, a standardlight source, a light sensitive device, means for alternately directingradiations from said furnace and said standard source to said lightsensitive device, a grid controlled rectifier arranged to control theenergize.-

-tion of said resistor, means for electrically connecting said lightsensitive device in the grid circuit of said rectifier so that said gridis positive with respect to the anode so long as the light rays from oneof said sources of radiation of said rectifier has a greater intensitythan the other of said sources.

6. In combination, a furnace having light emitting characteristicsvarying with its temperature, a heating resistor for said furnace,alight sensitive device, an arc rectifier having an anode and havinginput and output circuits for controllin the energization of saidresistor, connections for connecting said light sensitive device to saidinput circuit, a source of 'alternating current supply for said outputcircuit providing a voltage on said anode, a standard source of light, areflecting device having a plurality of movable reflecting surfaces,means for moving said surfaces in synchronism with said anode voltage toreflect light to said light sensitive device alternately from saidfurnace and from said standard, and means responsive to said lightsensitive device for impressing on the input circuit of said rectifier avoltage varying in phase relation with respect to said anode voltage inaccordance with the relative intensities of the light from said sources.

I. In combination, a furnace having light emit- -ting characteristicsvarying with its temperature, heating means for said furnace, an arcsectifler having input and output circuits for controlling said heatingmeans, a. light sensitive device, connections for connecting said lightsensitive device to said input circuit, a standard source of light, asource of alternating current for said output circuit, a reflectingdevice having a plurality of reflecting surfaces mounted for rotation tobring said surfaces into positions alternately to reflect light to saidlight sensitive device from said furnace and from said standard, meansfor rotating said reflecting device in synchronism with said outputvoltage so that when the anode of said rectifier is positive, light isreflected from said standard to said light sensitive device, and whensaid anode is negative, light is reflected from said furnace to saidlight sensitive device.

8. In combination, a furnace having light emitting characteristicsvarying with its temperature, a heating resistor for said furnace, asaturable core reactor for controlling the energization 'of saidresistor, an arc rectifier having grid and anode circuits forcontrolling the saturation of said reactor, a source of alternatingcurrent supply for said anode circuit, a. light sensitive deviceconnected to said grid circuit, a standard light source, a rotatablymounted reflecting device having a plurality of reflecting surfacesmovable to interrupt light alternately from said furnace and saidstandard and to reflect it on said light sensitive device, a motorconnected to said supply source for driving said reflecting device insynchronism with said supply source so that said light sensitive devicealternately receives light from said standard and said source, and atransformer connected to said light sensitive device 0 and said gridcircuit for impressing on said grid circuit a voltage varying in phaserelation with respect to said anode circuit in accordance with therelative intensities of the light from said light sources.

9. The method of controlling a tube having input and output circuits bya light sensitive device, a standard source of light and a variablesource of light, which consists in alternately directing light from saidstandard source and from 120 said variable source on said device,causing said device to generate a voltage varying in phase relation withrespect to said output circuit in accordance with the relative responseof said device to said sources, and causing said voltage to be 125impressed on said input circuit so as to render said tube conductivewhen one of said sources has a greater light intensity than the other ofsaid sources.

DAVID c. PRINCE. m

